This invention relates to an electronically scanned phased array antenna, and more particularly to a computing element for each antenna phase shifter element.
A phased array antenna is composed of a plurality of radiating elements positioned in a spaced-apart relationship. Such an antenna in a radar system is well adapted to electronic scanning techniques which permit a directional beam of electromagnetic energy to be moved rapidly from one direction to another by means of a plurality of phase shifter elements.
A phased array antenna may be optically fed from one or more radiant sources. Uncollimated and unsteered power from said radiant source incident upon an individual element passes through the phase shifting device and is radiated therefrom with a phase relationship determined by the setting of the individual phase shifter so as to provide the desired collimated and steered radiated phase front. Since said device is reciprocal, energy reflected from distant objects and impinging on the array in the form of substantially parallel rays will be focused by the array in a direction corresponding to the setting of the individual phase shifter.
In the prior art, phased array radar systems have used a central beam steering computer for calculating phase shifter command signals for each phase shifter element in an array antenna. These calculations consumed considerable computer time. Typically, there are thousands of phase shifter elements requiring a great number of wires to transmit the required phase shift information to these elements. In addition, the reliability of such systems was greatly affected by a single failure in the central beam steering unit.
Another approach in the prior art of phased array antennas for generating phase shift command signals involved a matrix distribution technique. Phase shift commands are calculated in two parts wherein one part is distributed along the X direction or rows of an X-Y matrix of phase shifter elements and the other part is distributed along the Y direction or columns. At each phase shifter there is co-located a simple adder that adds together the X and Y phase shift command parts forming the complete phase shift command word. Collimation correction factors have to be approximated using this shift command signal approach, but this approach reduces the amount of wiring required to distribute the command signals to the phase shifter, and therefore improves the system reliability. However, this approach is limited to uniformly spaced antenna array elements in a plane.
A serial data line and a clock line in the present invention further reduces the amount of wiring required to transfer phase shifter command signals to an array antenna and other techniques such as RF transmission may be utilized for such data and clock transfers. System reliability is further improved by not having a central beam steering computer that can fail. In addition, the distributed approach described in this invention does not require the elements to be uniformly spaced or located in a plane.